Named graph erroneous persists in query evaluation context

[sa-bpelakh]

On a query where a FILTER (perhaps other built-ins) immediately follows a GRAPH clause, the GRAPH is erroneously propagated into the FILTER evaluation, causing unintended behavior. For example, given the following input:

prefix  : <https://example.com/> .

:g1 {
  :Boris rdfs:label "Boris" .
  :Susan rdfs:label "Susan" .
}
:g2 {
  :Boris a :Person .
}

the query

PREFIX : <https://example.com/> 
SELECT ?p ?l WHERE {
  graph :g1 { ?p rdfs:label ?l }
  FILTER NOT EXISTS { ?p a :Person }
}

does not produce :Susan as expected.